The present invention relates to an optoelectric multichip module and a method of fabricating it using basically polymer materials.
Telecommunication systems using light propagating in different waveguides expand more and more today. There is a large interest in extending the optical networks even up to private homes and business offices, the so called local access network which is also called xe2x80x9cFibre To (In/From) the Homexe2x80x9d, xe2x80x9cFibre To (In/From) the Customer (Business)xe2x80x9d, etc. Also, there is a large interest in extending the use of optical networks in LANs, i.e. local area networks, used for interconnecting computers in a business estate and furthermore for communication inside computer equipment and for communication between computers and peripheral devices such as printers etc. In order to achieve this expansion, the costs of the components of the optical networks of course have to be reduced as much as possible. Very important costs are related to producing the optical transmitter and receiver modules including lasers, LEDs, etc. and other active or passive optical devices.
Only in a few cases attempts have been made to drastically reduce the costs when commercially manufacturing optoelectric and electrooptical modules. For example, the company Motorola has put a concept called xe2x80x9cOPTOBUSxe2x80x9d on the market. Some details thereof are disclosed in U.S. Pat. No. 5,659,648 for Knapp et al. In a multilayer structure based on a substrate made of polyimide optical signal layers are used as electrically isolating layers between electrically conducting metal layers. In FIGS. 1 and 2 the structures comprise waveguide cores 17, 18, . . . and 45, 46 of a polymer material which at their sides have metal strips in a central layer, the metal strips forming part of the waveguide cladding. Layers under and on top of the central layer are made of polyimide and constitute an overcladding and an undercladding. In the structure shown in FIG. 3 whole metal layers 52, 60 are in addition placed between the central layer and the polymer cladding layers. No details are given in regard to positioning electrical signal conductors.
It is an object of the invention to provide multilayer structures allowing both electrical and optical connections.
It is a further object of the invention to provide multilayer structures allowing electrical interconnections and optical connections having low losses.
It is a further object of the invention to provide a method of fabricating multilayer structures having electrical and optical connections which can be easily executed using a minimum number of processing steps.
A thin-film process is used for sequentially building a multilayer structure on top of a suitable substrate. In the multilayer structure at least on thin-film layer of a suitable polymer is used both as an electrically isolating layer separating signal conducting metal layers and as a layer of an optical waveguide. The materials of the thin-film structure are selected to be optically transparent to some suitable, selected light wavelength and have adapted refractive indices for this wavelength. Generally, signal conducting metal layers are located between and/or on top of and/or under the three thin-film layers forming the optical waveguide but the metal is etched away at the waveguide cores so that optical waveguides of the type having a refractive index difference between the core and the cladding material are obtained, i.e. the claddings are of a transparent optical material and are formed by portions of the bottom and top layers of the thin-film structure. Hence, electrical and optical interconnections can be integrated in the multilayer structure using a minimum number of polymer layers and the optical waveguides can be constructed having no metal layers for defining them or no metal layers in the direct vicinity of the waveguide cores. Various components can be mounted at the multilayer structure, such as lasers, photodiodes, electronic driver circuits for the optical devices, electronic logical and memory circuits. The components can e.g. be flip-chip mounted or wire bonded. For example a combined cable of ribbon type can be formed, accommodating both electrical conductors and optical waveguides.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the methods, processes, instrumentalities and combinations particularly pointed out in the appended claims.